In a modern internal combustion engine comprising a starter generator there occurs a change in the position of the tensioned strand and loose strand, which position is found in the direction of rotation of the belt in front of the driving belt pulley on the one hand and in the direction of rotation of the belt behind the driving belt pulley on the other hand. Depending on the state of operation, torque can be released at the driving belt pulley during the starting process, and consumed at the driving belt pulley during the driving process. In such a case, the loose strand should be loaded by a tensioning roller, and preferably two tensioning rollers are used directly in front of and directly behind the driving belt pulley. The change from torque release to torque consumption at the driving belt pulley corresponds to the change from torque consumption to torque release at the crankshaft belt pulley of the internal combustion engine.
EP 1 464 871 A1 proposes a double belt tensioning device wherein the pivot axis of the tensioning arms is positioned outside a polygon formed by the different axes of rotation of the belt pulleys. This has a number of disadvantages. Belt tightening devices of this type require a considerable amount of space which is not always available. The operation of positioning the belt is very complicated. Because of the long tensioning arms, long lever arms are provided which require high spring forces. Furthermore, the lever effect is very disadvantageous because, as a rule, the direction of the tensioning arm movement and the resulting direction of force of the belt deviate considerably from one another.
From DE 199 26 615 A1 there is known a tensioning device for traction means with two tensioning rollers wherein the axes of oscillation of the tensioning arms of the two tensioning rollers coincide with the driving axis of the driving belt pulley. The tensioning device comprises a flanged housing which supports a bearing shaft for a driving belt pulley. The device can be arranged at a driving machine in a finish-mounted condition, with the bearing shaft being connected to the driveshaft of the driving machine via a plug-in connection. Disadvantages of such a device include the driveshaft having two parts, with the bearing shaft of the driving belt pulley additionally having to be supported in the flange housing, as well as the design requiring a considerable increase in the overall length.